The present invention relates to gate valves and, in particular, a seat ring mounting for a tapered gate valve.
The copending application Ser. No. 605,277 entitled DOUBLE DISC GATE VALVE WITH REPLACEABLE SPACER RING, now abandoned, filed in the name of Ronald J. Anders and assigned to the assignee of the present invention, discloses a double disc gate valve wherein the individual gate pieces have inclined or tapered annular surfaces which engage similarly inclined annular tapered surfaces formed on the inner end of a cylindrical seat ring retained in a counterbore at the inner end of the flow passage adjacent the valving chamber. The discs translate vertically within the valving chamber as guided by outwardly extending tongues on the lateral vertical sides of the discs retained in grooves defined by laterally spaced pairs of vertical guide rails. The seat rings, because of the tapered seating surface, have a minor height section at their top, a major height section at their diametrically opposed base, and median height sections as measured in a horizontal plane. The seat rings also have an outer diameter related to the diameter of the seating interface. For small, low pressure valves, the lateral spacing between the pairs of guide rails is greater than the outer diameter of the seat rings such that the same can be directly lowered into the valve cavity and axially shifted into alignment with and seating position within the counterbores. For the larger high pressure valves, the same dimensional relationships can be maintained, however, the same is done only with a corresponding increase in the size of the pressure seal components. In other words, to obtain a lateral spacing between the guide rails greater than the diameter of the seat ring, the body size and the wall thickness necessary to contain the fluid increases thereby resulting in an unnecessarily larger, more costly construction.
The present invention overcomes the above-noted deficiencies by providing a seat ring mounting wherein larger seat rings can be accommodated without increasing body size. Herein, the lateral spacing between the pairs of guide rails is less than the outer diameter of the seat ring to maintain optimum body size and wall thickness. Normally, this relationship would cause interference in lowering the seat ring into the cavity. In other words, the projected continuation of the seat ring in assembly would interfere with the guide rails. Moreover, the grooves herein between the pairs of guide rails are only slightly wider than the minor height section of the seat ring. To accomplish installation of the seat ring in the present invention, crescent shaped spaced notches are formed in the guide rails coaxially with the flow passage and the seat ring counterbores. The notches have a diameter slightly larger than the diameter of the seat rings. With this construction it is possible, as hereinafter noted, to lower the seat ring between the guide rails and axially shift the ring through the space between the notches into its operative position. More particularly, the seat ring is initially rotated 90.degree. from its assembly orientation and the minor height section is laterally radially shifted into one of the grooves, the depth of penetration into the groove being sufficient such that the major height section lies inwardly of the inner edges of the opposed pair of guide rails. The seat ring is then vertically lowered until the axis of the seat ring lies in a common horizontal plane with the axis of the seat ring counterbore. In this position, the ring is laterally radially shifted into coaxial alignment with the notches and the counterbore, rotated 90.degree. to its assembly orientation, and axially shifted to its operative position in the counterbore. The ring is thereafter welded into place. With the ability to thus assemble the seat ring in a manner accommodating minimal body sizes, weight and cost savings are realized.